I can't tell you the number of times I've felt like I know absolutely nothing, that is ok and I've met a lot of people who go through it even if they've been doing this for 20+ years. What you feel as "knowing nothing" is the universe telling you the scope of what you are trying to master, it is meant to humble you, don't let it crumble you.
As for doing things from scratch, that isn't as easy as it has been in the past, look for a project doing something that speaks to what made you get into computers and engineering and see what you can contribute, sometimes the money aspect of this industry is what kills it's soul.
Take breaks, give your brain time to rest and get perspective, do things that are far, far away from anything to do with engineering and don't forget absolutely none of this at the end of the day is ever worth harming yourself over.